1. Field of the Invention
The present invention relates to a capacitor module, a power converter, and a vehicle-mounted electrical-mechanical system.
2. Description of the Related Art
Recently, a power semiconductor device capable of switching a large current has been developed. A power converter using such a power semiconductor device is able to supply electric power to a load, e.g., a motor, with high efficiency through the switching. Therefore, the power semiconductor device is widely utilized for driving motors of vehicle-mounted electrical-mechanical systems in trains, automobiles, etc. In a hybrid electric vehicle (HEV), particularly, an engine and an electric motor are combined with each other to realize outputting of higher torque from low rotation speed of the motor, storage of regenerative energy into a battery, as well as higher fuel economy and a reduction of CO2 in cooperation with an idle stop system (automatic engine stop system).
The power semiconductor device used in the power converter generates a loss at the time of switching. If the switching loss can be reduced, it is possible to reduce heat generated from the power converter, to cut the number of power semiconductor devices used, and to realize a power converter having a smaller size and a higher power density.
To reduce the switching loss, the switching time has to be shortened. In other words, an effective solution for reducing the switching loss is to increase a current time-dependent change di/dt and to realize faster switching. At the time of switching of a large current, however, a jumping voltage, i.e., an overvoltage in excess of the power supply voltage, is caused in the power semiconductor device based on L·di/dt, i.e., based on a abrupt current time-dependent change di/dt and a parasitic inductance L of wiring. Taking into account the jumping voltage, the power semiconductor device of the power converter employs a device that is resistant against a voltage higher than the power supply voltage. Reducing the parasitic inductance L of wiring is required to suppress the jumping voltage and to reduce the loss.
Parts of the power converter, of which inductances are to be reduced, are ones used in a circuit subjected to a momentary current change at the time of switching, i.e., a smoothing capacitor, a power semiconductor module using the power semiconductor device, and conductors used for connecting them. In those parts, it is important to reduce a total inductance, including part connecting portions as well.
Known techniques for reducing the inductance of a capacitor are disclosed in Patent Document 1 (JP, A 2001-268942) and Patent Document 2 (JP, A 2004-165309). With those known techniques, the inductance is reduced by arranging a plurality of capacitors on positive and negative conductors in the form of flat plates, which are opposed to each other with insulators interposed between them, and by connecting the capacitors such that electrodes of adjacent capacitors have different polarities, or by connecting a capacitor and a power semiconductor module in proximity relation so as to shorten the distance between them.